arrays – Swift – 如何存储在泛型类型的Array子类中

我想将这些子类的实例存储在一个数组中,这样它们就可以迭代并以相同的方式处理所有这些子类,但显然,没有办法将子类转换为泛型超类.

以下是一些说明问题的代码(您可以将其复制粘贴到操场中以查看结果)：

// Lets create regular classes
class Fruit {
    var text: String { return "I am some Fruit" }
}

class Apple: Fruit {
    override var text: String { return "I am an Apple" }
}
class Orange: Fruit {
    override var text: String { return "I am an Orange" }
}

// This obvIoUsly works:
let test1: Fruit = Apple()
let test2: Fruit = Orange()


// Let's create some generic class
class Tree<T: Fruit> {
    let fruit: T
    init(fruit: T) {
        self.fruit = fruit
    }
}

// Subclasses from the generic class (these work)
class AppleTree: Tree<Apple> {
    convenience init() {
        self.init(fruit: Apple())
    }
}

class OrangeTree: Tree<Orange> {
    convenience init() {
        self.init(fruit: Orange())
    }
}

// This works:
let tree: Tree<Fruit> = Tree(fruit: Apple())
tree.fruit.text               // "I am an Apple"

// This works:
let appleTree1: Tree<Apple> = AppleTree()
appleTree1.fruit.text     // "I am an Apple"

// This fails: "CAnnot convert value of type 'AppleTree' to specified type 'Tree<Fruit>'
let appleTree2: Tree<Fruit> = AppleTree()

// This works:
let fruitArray: [Fruit] = [Apple(),Orange()]

// THIS IS MY GOAL:
// This fails: "CAnnot convert value of type 'AppleTree' to specified type 'Tree<Fruit>'
let treeArray: [Tree<Fruit>] = [AppleTree(),OrangeTree()]


// Let's try with a generic subclass
class FruitTree<T: Fruit>: Tree<T>{}

// This works:
let genericTree: Tree<Fruit> = FruitTree(fruit: Apple())

// Let's try with a generic but more concrete subclass
class GenericOrangeTree<T: Orange>: Tree<T>{
    convenience init() {
        self.init(fruit: Orange() as! T)
    }
}

// This works:
let genericOrangeTree1 = GenericOrangeTree(fruit: Orange())
let genericOrangeTree2 = GenericOrangeTree()

// This fails: CAnnot invoke initializer for type 'GenericOrangeTree<Orange>' with an argument list of type '(fruit: OrangE)'
let genericTree2: Tree<Fruit> = GenericOrangeTree(fruit: Orange())

// Again,this fails: "CAnnot convert value of type 'GenericOrangeTree<Orange>' to specified type 'Tree<Fruit>'
let genericTreeArray: [Tree<Fruit>] = [GenericOrangeTree()]

我试图做的是通过treeArray变量在示例代码中说明的.

我不明白为什么代码失败时会失败.我的直觉说这应该有效,我无法找到解决这个问题的方法.

TL; DR：我有一个带有一些子类的Generic类,我想要一个填充了子类的Generic类的数组,但编译器抱怨.